Numerous industrial processes, and especially processes in refineries and processing plants produce gas streams containing considerable amounts of hydrogen. While some of the gas streams are hydrogen production streams (e.g., a hydrogen containing stream from which hydrogen has not been removed, and especially streams produced by a steam reformer/shift converter system), other gas streams are offgas streams (typically a hydrogen containing stream from which a portion of the hydrogen has previously been removed in a reaction consuming hydrogen or other hydrogen sequestering process).
Hydrogen contained in hydrogen production streams can be recovered using various methods well known in the art. For example, Doshi et al. employ a membrane assembly to produce from a feed gas a hydrogen-rich permeate, which is then fed into a hydrogen pressure swing adsorption unit to generate purified hydrogen as described in U.S. Pat. No. 4,863,492. Alternatively, as described in U.S. Pat. No. 5,152,975 to Fong et al., natural gas is subjected to partial oxidation and shift conversion to form a hydrogen production stream that is then directly routed into a hydrogen pressure swing adsorption unit to generate purified hydrogen.
Similarly, hydrogen contained in offgas streams can be recovered using numerous methods well known in the art. For example, Fong et al. describe in U.S. Pat. No. 5,152,976 partial oxidation and shift conversion of various offgases to form a hydrogen production stream that is then routed into a hydrogen pressure swing adsorption unit to generate purified hydrogen. Thus, it should be recognized that it is generally known to separately purify hydrogen from a hydrogen production stream or an offgas stream by employing separate hydrogen PSA units for each of the streams. However, it has apparently not been recognized that hydrogen can be purified from both a hydrogen production stream and an offgas stream employing a common hydrogen PSA unit.